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The dependence of the Rosseland Mean Opacity (RMO) on the equation of state and the number of included atomic levels of iron ions prevalent at the solar radiative/convection boundary is investigated. The 'chemical picture' Mihalas–Hummer–Däppen (MHD) equation-of-state (EOS), and its variant QMHD–EOS, are studied at two representative temperature–density sets at the base of the convection zone and the Sandia Z experiment: (2 × 106 K, 1023/cc) and (2.11 × 106 K, 3.16 × 1022/cc), respectively. It is found that whereas the new atomic data sets from accurate R-matrix calculations for opacities (RMOP) are vastly overcomplete, involving hundreds to over a thousand levels of each of the three Fe ions considered – Fe  xvii , Fe  xviii , Fe  xix – the EOS constrains contributions to RMOs by relatively fewer levels. The RMOP iron opacity spectrum is quite different from the Opacity Project distorted wave model and shows considerably more plasma broadening effects. This work points to possible improvements needed in the EOS for opacities in high-energy–density plasma sources. [ABSTRACT FROM AUTHOR]